But, but, but: As of now, anti-drone technology is still hugely limited, experts say. None of the hundreds of devices on the market will work against every drone, and many don't work at all. "A lot of this is snake oil," says Francis Brown, CTO of Bishop Fox, a security firm.

Net guns can be defeated with a simple cage built to protect a drone's rotors. Jammers and spoofers — which break a drone's connection to the operator or pretend to be the operator — can't overpower some drones.

If they do — or if a conventional weapon finds its mark — you've got a new problem: a plunging, spinning, battery-powered drone, perhaps over a parade or stadium.

Jammers cause another type of collateral damage: they can take down radio, GPS, and wi-fi nearby — which is why the FCC almost never allows them to be used.

What's happening: Police departments are acquiring these devices anyway — even though just 4 federal agencies are currently authorized to bring down drones.

The L.A. County Sheriff and Oceanside Police, near San Diego, own DroneKillers, a device that overloads airborne drones with a digital signal so that they are forced to land.

IXI, the California company that makes the DroneKiller, says a third agency in Nevada is about to buy one.

Andy Morabe, IXI's marketing director, argues that these 3 agencies have been cleared to use counter-drone technology in a signed letter from the FBI director. But both California police departments say they have no such letter.

For now, confusion and legal hurdles are preventing use of the devices.

The L.A. County Sheriff's Department says neither of their two DroneKillers has ever been fired, and Oceanside's has been shelved for over a year.

"Any agency that's purchased any counter-drone system, there's no way for them to legally deploy it," says Jason Snead, a policy analyst at the Heritage Foundation.

If that happens, a lack of national standards and rigorous testing — plus a ballooning market — means buyers have to wade through a sea of confounding options to find something that works.

2. Space robots that think for themselves

Curiosity, on Mars. Photo: NASA/JPL-Caltech/MSSS/Andalou/Getty

From Earth, you want to pick something up from the surface of the Moon. Using a joystick, you control a grabber — but you keep missing. It's the delay: It takes light nearly 3 seconds to get to the Moon and back, and the control signal even longer, Kaveh writes.

The big picture: This is a fundamental, insurmountable hurdle to moving stuff around in space if you're not there. The farther you are from Earth, the longer the communications delay — nothing, after all, moves faster than light.

One workaround is to just move really slowly. Fine if you're picking up a rock; not that great if you're trying to build a structure or repair something from afar.

A more powerful approach is to build as much autonomy as possible into the robot doing the job. That means that instead of telling it to move the grabber forward 2 inches, down 4 inches, and grab, you can just tell it to pick up the rock.

What's happening: Several startups, as well as NASA, are trying to find the right combination of human control and autonomy that would allow robots to do complex tasks in space. Full autonomy isn't an option for now — today's artificial intelligence isn't up to the job.

Favorite thus far: "The Glass Castle," Jeannette Walls (I was admittedly late to the party when I read this memoir earlier this summer. I've spent my whole life on the coast, and this took me to the heart of "left-behind" parts of the country.)

Reading now: "These Truths," Jill Lepore (I started this last night after a glowing review from my boyfriend, who said, "It's all of U.S. history, but told like a story.")

On deck: "Super Pumped: The Battle for Uber," Mike Isaac (The WSJ's John Carreyrou is calling this a must-read if you want to understand the modern Silicon Valley, so obviously I'm going to read it.)